1. Technical Field
This disclosure relates to machine-readable indicia and symbols which encode information therein, and to printers to print machine-readable indicia and symbols and readers to read machine-readable indicia and symbols.
2. Description of the Related Art
Machine-readable symbols are ubiquitous, used on labels applied to various goods in stores, and used on objects such as equipment, pallets and even railcars. Machine-readable symbols provide an inexpensive way to encode information, typically about the good or object, in a form that is easy to extract using automatic data collection devices such as machine-readable symbol readers (i.e., imagers, scanners). Machine-readable symbol readers are commonly referred to as scanners or barcode scanners, without regard to whether such take the form of imager employing ambient light or flood illumination or scanners which typically employ a photodiode or the like and a narrow scanning beam of illumination such as a laser.
Machine-readable symbols are typically formed of a number of symbol characters, which are selected from a symbology. Each symbol character is defined by a set of marks (e.g., bars and spaces). A symbology defines a mapping between symbol characters and human-readable or human-comprehensible symbols, for instance alphanumeric characters (e.g., full ASCII set) or characters from non-English alphabets (e.g., Greek, Cyrillic, Chinese, Kanji). The symbology may even define a mapping between certain symbol characters and commands or operations (e.g., shift, start, stop). There are a large number of existing symbologies, for example Universal Product Code (UPC)/European Article Number (EAN), Code 39, Code 128, Code 93i, Codabar, EAN/JAN-13, PDF 417, DataMatrix Code, MaxiCode.
Machine-readable symbols take a variety of forms. For example, the most common type of machine-readable symbols are one dimensional or linear machine-readable symbols, commonly referred to as barcode symbols. Linear machine-readable symbols are typically formed of combinations of bars and spaces, although any to contrasting colors may be employed. Early linear symbols employed a binary symbology, for instance binary coded decimal. Newer linear symbologies achieve higher density (i.e., amount of encoded information per unit area) typically by encoding information in the relative distances between leading edges and/or trailing edges of successive bars and/or spaces.
Also for example, two dimensional symbols such as area or matrix machine-readable symbols or stacked machine-readable symbols are becoming increasingly more common due to their higher information encoding density relative to linear machine-readable symbols. Area or matrix machine-readable symbols typically employ two dimensional arrays of marks (e.g., hexagons) where information is encoded in the pattern of the marks. Stacked code machine-readable symbols typically employ multiple rows of linear machine-readable symbols, the increase in density resulting from reducing the space that would otherwise be required between separate linear machine-readable symbols.
Efforts to further increase information density include attempts to define and use multi-color symbologies. Such attempts employ three or more colors to encode information. The result of a recent attempt is the high capacity color barcode technology developed by Microsoft Corporation. Such employs either a 4 color palette or an 8 color pallet to form two dimension machine-readable symbols. Each symbol is composed of an array of rows and columns. Each cell of the array is divided diagonally, and each portion of the cell is a respective color selected from the particular palette of colors to encode information.
While typically not readable by the average human, the marks which form a machine-readable symbol are typically visually perceptible by humans. For example, humans will see a pattern of dark bars and white or light spaces, but will not likely be capable of discerning the information encoded in the pattern of marks. Such is true whether the machine-readable symbols are encoded using a standard two color symbology (e.g., black bars, white or light spaces) or using a multi-color symbology.
New approaches to producing and/or reading machine-readable symbols, particularly high density machine-readable symbols are desirable to allow automatic encoding and collection of information.